The present invention relates to a computer system having a workstation or a server and, more particularly, to high speed accessing of files stored in a magnetic disk subsystem.
CPU performance has drastically improved in recent years with the resultant prominent improvement in the workstations or servers. As compared with the improvement in the CPU performance, however, the improvement in the I/O performance, especially, in the access speed of files stored in a magnetic disk subsystem cannot be said to be sufficient. This insufficiency is caused mainly by the bottlenecks in (1) the access speed in a secondary memory subsystem such as the magnetic disk subsystem and (2) the speed of an I/O bus interface.
For high speed file access by eliminating the secondary memory bottleneck, an array disk system has a plurality of magnetic disk subsystems "disk drives" or merely "disks", so that high speed file access may be realized by operating the individual disks in parallel. The other speed bottleneck of the I/O bus interface is to be eliminated by using a high speed interface for connection with the I/O bus.
FIG. 46 shows a construction of an array disk system, and FIG. 47 shows a synchronized time chart of the array disk system file for reading. FIGS. 46 and 47 show an example, in which each stack of stacks O-n is constructed of four disks hd0-hd3, but this disk number may be more or less. The operations of the array disk system will be described with reference to FIGS. 46 and 47.
When an array disk system 300 receives a read instruction from a host CPU system 400, its internal controller starts disks hd0 to hd3 of a stack 0 substantially simultaneously for reading data blocks. Each disk of the stack 0 reads the corresponding data block from a magnetic disk media after seek and rotational delay. The data blocks 0 to 3 read from the disks are individually stored in different FIFOs (310 to 313) respectively. These reading operations are executed independently and in parallel for the disks hd0 to hd3 of the stack 0 so that the total reading procedure is speeded up as compared to reading from only one disk. Next, data blocks 0 to 3 are individually transferred in a time sharing manner consecutively to a buffer 330 through a high speed bus i-Bus (internal bus) 320 in the system. This buffer 330 arrays the data blocks 0 to 3 and transfers them to the host CPU system 400 through SCSI bus interface I/F 340 and a high speed SCSI bus 160. After this, if a next read instruction is issued, the internal controller in the array disk system starts the read of the disk of a stack, from which the data block is to be read. The array disk system realizes high speed file access by repeating a series of such operations.
The array disk system is exemplified by Japanese Patent Laid-Open No. 41044/1989 entitled "Data Transfer System" or Japanese Patent Laid-Open No. 21525/1989 entitled "Magnetic Disk Control System".